Device for monitoring anatomical unit or a radiotherapy unit

ABSTRACT

The invention concerns a device for monitoring an imaging or radiotherapy unit ( 1 ) for treating members of the human body subject to displacements related to movements of the diaphragm. The invention is characterized in that said monitoring device is designed to enable, in a prior preparation phase, to store two values, called rest value and triggering value, respectively representing, for each patient, of his suspended ventilatory level and an inhalation or exhalation ventilatory level, triggering acquisition of images or irradiation, then, during the real monitoring of the unit ( 1 ), in commanding an image or irradiation acquisition, once the correspondence between the measured value of the suspended ventilatory level and the stored rest value has been established, and only when the correspondence between the measured respiratory value of the patient and the stored triggering value has been subsequently established. Additionally, said monitoring device comprises means ( 11 ) for displaying the respiratory curve of the patient, which can be viewed by him, and whereon are physically represented the rest and triggering values.

The invention relates to a device for driving an anatomical imaging unitor a radiotherapy unit for the purpose of treating organs in the humanbody, and more specifically, organs that are subject to displacementsrelated to the movement of the diaphragm, and the position of whichtherefore varies as a function of thoracic expansion.

In the field of radiotherapy, x-ray scanners are now integrated into theservices, and have resulted in a fundamental transformation ofpreparation procedures. Helical acquisition has in fact reduced thelength of the examination and allowed both a greater number of slicesand a low level of reconstruction thickness. These high-quality imageshave delighted users in respect of both exploration for the purpose ofcontouring and virtual simulation. The shape of the radiation beams hasthus been able to be deduced from the shape of the target volume, andthe three-dimensional calculation of the dose distribution has offeredanalysis tools that favour dosimetric optimization.

Conversely, the precision introduced by the simulation procedure datahas made it essential to reduce the daily positioning error. Thus,customized supports made prior to scanner acquisition are now usedduring the preparation procedure and at all treatment sessions. In spiteof that, assessments have nonetheless demonstrated the limitations ofdaily precision and have led to the adoption of margins adapted to eachsituation.

It is more difficult, on the other hand, to take account of diaphragmmovements and therefore of the organ to be displayed and treated betweenthe different preparation phases and at each treatment session. Of allthe sources of mobility, in fact, breathing causes the most significantdisruption. The most significant displacements, as has been shown by anumber of studies, are found near the diaphragm and may reach as much as4 cm, and are therefore far in excess of the daily repositioning error.

In order to find a solution to this problem it has been envisaged toevaluate the ranges of movement of the organs with breathing, and toincorporate these ranges in the dosimetric plan. However, it has seemedunrealistic to apply corresponding margins without running the risk ofcreating major complications, for example in the lungs when treatingthoracic tumours, and of compromising the quality of patient care.

To this data it should be added that the quality of the treatment alsodepends on the skill of the operators who are not always necessarily thesame during a series of treatment sessions.

In practice, it follows from what has been said above that thepotentialities related to virtual simulation are not exploited in anoptimum way, and that, in the context of radiotherapy, radiation dosesare currently of necessity relatively small, and cases of therapeuticcomplications, such as radiation-induced lung diseases during thetreatment of thoracic tumours, unfortunately still far too numerous.

The purpose of the present invention is to overcome the above-mentioneddrawbacks of anatomical imaging and radiotherapy and its main purpose isto provide a drive device that can bring about a significant reductionin the geometrical margins as currently introduced, and thereby allowclear and accurate reconstructions in three dimensions, can almosteliminate the risks of complications such as radiation-induced lungdiseases, and allow the doses administered to be increased.

A further objective of the invention is to provide a device that allowspatients to take responsibility for themselves and to experience thetreatment sessions in a calmer frame of mind.

Another objective of the invention is to provide a device that consistsof a very “light” piece of equipment with a low cost price and smallspace requirement, which is very easy to employ.

Another objective of the invention is to provide a device that allowsimage acquisition or radiation triggering to be controlledautomatically.

To this end, the invention applies to an anatomical imaging orradiotherapy unit drive device, comprising:

-   -   means for measuring the thoracic expansion of patients,    -   a control unit connected to measurement means so as to receive        signals emitted by them, and to the imaging or radiotherapy unit        so as to drive it, said control unit:    -   comprising means for storing so-called resting and trigger        values, representing respectively, for each patient, his level        of resting ventilation and an inhalation or exhalation        respiratory level, for triggering image acquisition or        radiation,    -   being programmed so as to control an image acquisition or        radiation, once the correspondence is established between the        measured value of the resting ventilation level and the stored        resting value, then only when the correspondence is subsequently        established between the measured value of the patient's        respiratory level and the stored trigger value, and so as to        stop the acquisition or radiation when this second        correspondence is no longer respected,    -   and means for viewing the patient's breathing curve that are        connected to the control unit and placed so as to be viewable by        said patient, said control unit being adapted so as to generate        the display on said viewing means of the resting values and        trigger values.

Such a drive device is therefore designed to be able to operate in thefollowing way:

-   -   in a prior preparation phase:        -   the patient's current metabolic volume is measured, and a            value, known as the resting value, and representing his            resting ventilation level, is stored        -   and when the patient is in resting respiratory conditions,            he is asked to inhale or exhale, the respiratory level is            determined for which the acquisition or radiation will be            triggered, and a value, known as the trigger value and            representing this respiratory level, is stored        -   and at each treatment session, or at each subsequent imaging            session intended for example to allow the effects of a            treatment to be monitored, the patient's respiratory level            is continuously measured and:        -   when the patient is at rest, his resting ventilation level            is compared with the stored resting value,        -   when there is a correspondence between the measured and            stored resting values, a radiograph acquisition or radiation            sequence is initiated consisting in authorising triggering            only when the patient has stopped his breathing at a            respiratory level corresponding to the stored trigger value            and in bringing it to an end when the patient ceases to hold            his breath,        -   and the resting/trigger cycles are repeated until the            scheduled radiation time for the session has elapsed, or            until all the radiographs required have been made.

The device according to the invention therefore allows, in a priorphase, two values to be stored representing respectively the patient'sresting ventilation level, and the pulmonary volume when inhaling orexhaling of the patient, in respect of whom it has been decided totrigger the radiography or radiation.

Subsequently, at each imaging or treatment session, triggering is onlyinitiated if the patient, previously in a situation of breathing atrest, has managed to stop his breathing at the required breathingtrigger level.

Triggering therefore only occurs when the following two conditions aremet: an initial condition which makes it essential for the patient tobreathe normally before holding his breath, and a final condition whichmakes it essential that the breath is held with a level of breathingthat is always identical both at each radiograph acquisition session andat one and the same treatment session, and from one treatment session toanother.

The necessity of meeting these two conditions, together with the factthat the two values calculated in the previous imaging phase are storedin a patient dedicated file, means the achievement of completereproducibility of the apnoea conditions and complete repetitivity ofradiation or complete similarity of the conditions in which thesuccessive radiographs are taken.

In practice, and in the first place, the fact that all the radiographsare taken in strictly identical conditions of breath holding, leads tovery accurate and very clear reconstructions in three dimensions, whichallow the theoretical margins introduced during the reconstructions tobe reduced.

Moreover, at radiotherapy sessions, the fact that the radiation isapplied when the patient is holding his breath in other words when theorgan to be treated is not subject to any movement resulting frombreathing, together with the perfect reproducibility of these apnoeaconditions, also allows the theoretical margins introduced to takeaccount of respiratory movements to be significantly reduced.

It should be noted that the pure and simple elimination of thesetheoretical margins may occur if it is decided not to take account oftransverse cardiac movements or any thoracic relaxation. On theassumption that these elements are taken into account, it means thatthese theoretical margins may be reduced to values of about 2 to 3 mm,in the treatment of thoracic tumours.

The result of the above-mentioned advantages relating to the inventionis that the device according to the invention leads to a new situationwhere the risk of therapeutic complications can be reduced to the pointof no longer presenting an obstacle to plans to increase doses.

Furthermore, and in an essential way, once the prior preparation phaseis implemented, and at each subsequent session, the patient is able toview his respiratory curve on which the stored resting and triggervalues are embodied. This viewing by the patients of their respiratorycurve in fact allows them to take responsibility for and to involvethemselves in controlling the level of apnoea. In practice, takingresponsibility in this way tends to make the patients much moreattentive and calmer.

Moreover, with regard to this calmness, it should be noted that thepatient alone is in control of the moment when he will trigger hisapnoea, from the moment when he is breathing normally. As a consequence,he is able to conduct each session at his own pace, without any stress.

It should be noted, additionally, that this involvement of the patientsconstitutes one of the basic principles for operating the drive deviceaccording to the invention, since it authorises, without any danger ofstress for these patients given that they themselves are managing theoperation of the sessions, the triggering of these radiographacquisition or radiation sessions, for ventilation levels in excess ofthe resting ventilation level.

Because of this, in fact, practitioners benefit, in respect of eachpatient, from a wide range of respiratory levels in determining apositioning of the target-volume that allows optimum acquisition andtreatment in perfectly reproducible conditions.

It should be noted, in this regard, that it has already been envisaged,as described in documents WO 98/52635 and U.S. Pat. No. 5,067,494, totrigger the radiation of a target-volume when the patient is in aposition of holding his breath at a given respiratory level.

However, current devices for implementing this principle consist of verycumbersome pieces of equipment, such as the artificial respiration unitdescribed in WO 98/52635.

Moreover and above all, the technique employed still consists in using aclosed respiratory circuit which leaves the initiative for stopping thepatients breathing for the purpose of radiation to the operator alone.

For this reason, and in the first place, perfect reproducibility of thetrigger conditions cannot be guaranteed given the fact that it dependson operator involvement.

Moreover, since trigger management is incumbent on the operator alone,these triggers can only be prompted at respiratory levels comparable tothe resting respiratory level, in the absence of which patients couldnot withstand full treatment sessions.

According to one advantageous embodiment, the means for measuringthoracic expansion include a spirometer. The spirometer is, indeed, theonly measurement means that makes it possible to provide a correlationbetween thoracic expansion and the corresponding volume of air.

Moreover, the control unit advantageously includes, for each patient,means of storing a trigger value representing an inhalation level. Infact an inhalation phase apnoea, leading to the lungs increasing in sizeand to a reduction in their density, has also proved to bring about areduction in the target volume which helps protect the lung whentreating thoracic tumours. Moreover, inhalation also causes a reductionin the pulmonary tissue and consequently the risks of lesions throughthe irradiation of healthy tissue surrounding the target volume.

Additionally, increasing the volume of the lungs is salutary for thenumerous patients breathing inadequately on account of their tobaccoaddiction, since for some it may constitute a source of success in theirradiotherapy.

Moreover, and to advantage, according to the invention, the drive deviceincludes support means for the spirometer that are able to keep it in awithdrawn position relative to the patient's head, said spirometer beingconnected to an oral nozzle via a breathing tube on which is interposedan interchangeable bacterial filter.

This positioning of the spirometer allows the patient to stretch out inthe dorsal decubitus position, with his hands crossed on top of hishead, so that the thorax of this patient is totally disengaged, thusallowing the positioning of oblique beams. Moreover, the interchangeablebacterial filter is intended to avoid any risk of contamination betweenpatients.

According to one advantageous embodiment, the control unit comprisesmeans for storing a range of resting and trigger values, eachrepresenting a measurement margin relative to the measured resting andtrigger values.

The objective of this measurement margin is to take account of possiblevariations in the resting ventilation level and apnoea level which canbe estimated at about 5% of the vital capacity for a stoppage in deepinhalation.

According to another advantageous embodiment which may or may not beadded to the one mentioned before, the control unit is programmed, withview to controlling an acquisition or radiation, so as to measure inreal-time the actual values of the patient's resting ventilation leveland to calculate at each moment, as a function of the measured restingvalue, a trigger value redefined relative to said resting value.

According to this embodiment the trigger value at a moment t issystematically redefined relative to the resting value measured at amoment t-ε, therefore a real resting value, and the drive device istherefore then designed so as to take account of possible drifts of theresting ventilation level, resulting for example from variations intemperature, humidity etc.

Furthermore, and to advantage, the control unit is programmed so as toauthorise the triggering of the acquisition or radiation after a pre-setlapse of time following the moment when the correspondence isestablished between the stored and measured trigger values. The purposeof this time lapse is to make sure that the patient fully maintains hisapnoea, in order particularly to avoid an untimely triggering. It alsomakes it possible to take account of either the inertia of the imagingor radiotherapy unit, or the operator response time.

Furthermore, the drive device includes to advantage means for viewingthe patient's respiratory curve connected to the control unit and placedso as to be viewable by the operator, and means for communicatingbetween the operator and the patient that are able to allow said patientto be informed of the moment when the measured and stored resting valuescorrespond.

These viewing means allow the operator to check the proper operation ofthe session and to inform the patient, after each apnoea, of the momentfrom which he recommence his apnoea.

To advantage, the communication means include, additionally, a controlbutton to switch on a light on the patient's viewing means.

Furthermore, for the purposes of automation and eliminating any risk ofhuman error, and to advantage, the control unit is programmed so as toactivate the imaging or radiotherapy unit automatically when there is acorrespondence between the measured and stored trigger values.

However, for the purposes of security, and to advantage, the drive unitincludes an intermediary housing interposed between the control unit andthe imaging or radiotherapy unit, and comprising an emergency stopbutton that can be activated by an operator.

Other characteristics, purposes and advantages of the invention willemerge from the following detailed description with reference to theappended drawings which show a preferential embodiment thereof as anon-restrictive example. In these drawings:

FIG. 1 is a block diagram of a drive device in accordance with theinvention,

FIG. 2 is a graph showing the respiratory curve of a patient undergoingtreatment, as shown to said patient and to the operator.

The device shown by way of example in FIG. 1 is adapted to drive aradiotherapy unit 1 intended for the treatment of thoracic tumours andcomprising a particle accelerator.

This drive device comprises, in the first place, a spirometer 2 of thepneumo-tachograph type comprising a respiratory flow differentialpressure sensor integrator, and adapted to deliver an electrical signalrepresenting the volume of air corresponding to the thoracic expansion.

This spirometer 2 is fixed via any means 3 known per se to the head ofthe treatment table 4 so as to be positioned beyond the head of thepatient during preparation and treatment sessions.

This arrangement makes it possible, in fact, as shown in FIG. 1, for thepatient to stretch out in the dorsal decubitus position with his handscrossed on top of his head, in other words in a position that totallydisengages the thorax, allowing the positioning of oblique beams.

The spirometer 2 is additionally connected to an oral nozzle 5 via aflexible pipe 6 on which is interposed an interchangeable bacterialfilter 7.

The spirometer 2 additionally incorporates means for heating the sensorto a stabilised temperature, such as an electrical resistance, keptpermanently supplied with power during the preparation and treatmentsessions and intended to eliminate the humidity produced by thepatient's breathing which may cause errors in the value of thecalculated volumes due to the modification of the characteristics of theelement constituting the drop in pressure.

Moreover, since this spirometer is dedicated to radiotherapy (or toimaging), it is not possible to disconnect the patient during thesession, with a view to setting, with each new measurement, and as isrequired by any conventional spirometer, the differential pressureintegrator to zero. The spirometer according to the invention istherefore equipped with a specific system, such as a bypass circuit thatcan be controlled by the operator, and which allows the differentialpressure integrator to be isolated during each zero flow reading.

The device additionally includes a micro-computer 8 to which a monitor 9is connected. This micro-computer 8, placed in proximity to the controlconsole is connected to the spirometer 2 via a connection 10, so as toreceive a signal representing the patient's respiratory curve as afunction of the time which can be viewed on the monitor 9.

The device additionally includes a pair of goggles 11 comprising atleast one liquid crystal screen, connected by a cable 12 to an interfaceoutput of the micro-computer 8, and intended to be worn the patient soas to allow him to view his respiratory curve.

The device comprises finally a control connection 13 connecting themicro-computer 8 and the radiotherapy unit 1 allowing the latter to becontrolled automatically. On this link 13 is additionally interposed anintermediary housing 14 intended to be placed in proximity to thecontrol console, and comprising an emergency stop button and a poweron/off light allowing the operator to verify that operations areproceeding normally.

Radiotherapy treatments using the drive device according to theinvention take place as described below.

In the first place, the radiotherapy preparation procedure comprises,prior to any examination, the making of a customised hemi-corporalsupport in polyurethane foam.

Throughout the preparation and treatment stages described hereinafter,the patient, placed in his support is stretched out on the treatmenttable 4 in the dorsal decubitus position, with his hands crossed on topof his head, so as to disengage the totality of the thorax. Moreover, heis taken care of by the radiotherapy dedicated scanner.

Furthermore prior to any preparatory or treatment session, thespirometer 2 is calibrated so as to guarantee the reproducibility of thevalues measured from one session to another.

The first preparation stage, apart from the conventional stages ofcontouring the target volume and determining the radiation beams and,generally, the treatment to be administered, also consists indetermining and storing two values which will condition the operation ofthe treatment sessions.

The first value is determined when the patient breathes normally, atrest, by measuring his current metabolic volume, and storing a restingvalue Nr representing the resting ventilation level of this patient.

The second value is, for its part, determined when the patient inhalesdeeply, by raising the level of inhalation in respect of which thetumour is located in an optimum position for radiograph acquisition andradiotherapy treatment. The corresponding stored value called thetrigger value Na level corresponds to the inhalation level in respect ofwhich radiograph acquisition and radiation will subsequently betriggered at all sessions.

The values are additionally stored with a measurement margin that isparameterisable as a function of the breathing capacity of the patients,this measurement margin being intended to make it possible to takeaccount of any variations in the resting ventilation and apnoea level.

Furthermore a patient dedicated file, intended to integrate alltreatment related parameters and data with a view to ensuring perfecttraceability, is used for storage.

Once the preparation stage has been implemented, and at all treatmentsessions, the control unit is programmed to continuously calculate thepatient's respiratory curve as a function of the signal delivered by thespirometer 2 and to display a graphical representation of this curve onthe screens of the monitor 9 and the goggles 11.

Furthermore, as shown in FIG. 2 the resting Nr and trigger Na values arealso displayed on the screens with their measurement margin.

At each session, when the patient's breathing is normal, in other wordswhen his resting ventilation level coincides with the resting value,said patient is informed by the operator, for example by switching on alight, for example a green light, on the screens of the goggles 11, thathe may trigger an apnoea.

From this moment on, the patient is able to take full responsibility andto trigger this apnoea when he so wishes. Moreover since he can see hisrespiratory curve in front of him this patient is easily able to controlhis apnoea level so that it coincides with the trigger value Na.

Once this level of apnoea is obtained and after stabilisation for aperiod of about 1 s, the control unit 8 is programmed to triggerradiation for a length of time corresponding to the time during whichthe patient maintains his apnoea or for a period of time set by theoperator at the end of which a light, for example a red light, isswitched on on the screens of the goggles 11. The patient is then ableto resume his normal breathing so that his resting ventilation levelonce again coincides with the resting value Nr.

According to the invention device, the radiotherapy unit 1 is thereforedriven automatically with remarkable repetitivity and reproducibility oflevels of shot and the patient, who is involved in the sessions,experiences them in a much calmer frame of mind.

1. A device for driving a radiotherapy unit for the purpose of treatingorgans in the human body subject to displacements related to movementsof the diaphragm comprising: a spirometer for measuring the pulmonaryvolume of patients, support means for the spirometer that are able tokeep it in a withdrawn position relative to the patient's head, saidspirometer being connected to an oral nozzle via a breathing tube onwhich is interposed an interchangeable bacterial filter, a control unitconnected to the spirometer, and to the radiotherapy unit so as to driveit, said control unit comprising: means for storing so-called restingand trigger values, representing respectively, for each patient, hislevel of resting ventilation and an inhalation or exhalation respiratorylevel, means for viewing the patient's breathing curve that areconnected to the control unit and placed so as to be viewable by saidpatient, said control unit being adapted so as to generate the displayon said viewing means of the resting and trigger values, said controlunit being programmed so as to perform the following steps: when apatient is breathing at rest, the value of the patient's respiratorylevel measured by the spirometer is compared with the stored restingvalue, only when a first correspondence is established between themeasured value of the patient's respiratory level and the stored restingvalue, the patient is subsequently asked to initiate a voluntary apneawhich level is controlled by the patient himself by viewing hisbreathing curve on said means for viewing, so that a radiation sessionis initiated consisting of: when the patient is performing saidvoluntary apnea, radiation is triggered immediately by the control unitonly when a second correspondence is established between the measuredvalue of the patient's respiratory level and the stored trigger value,and said radiation is terminated immediately by the control unit whenthe patient ceases his voluntary apnea with this second correspondencebeing no longer respected.
 2. The drive device according to one of claim1, wherein the viewing means consist of goggles equipped with at leastone liquid crystal screen.
 3. The drive device according to claim 1,wherein the control unit includes, for each patient, means for storing atrigger value representing an inhalation level.
 4. The drive deviceaccording to claim 1, wherein the control unit comprises means forstoring a range of resting trigger values, each representing ameasurement margin relative to the measured resting and trigger values.5. The drive device according to claim 1, wherein the control unit isprogrammed, for the purpose of controlling an acquisition or radiation,so as to measure in real-time the actual values of the patient's restingventilation level and to calculate at each moment, as a function of themeasured resting value, a trigger value redefined relative to saidresting value.
 6. The drive device according to claim 1, wherein thecontrol unit is programmed so as to authorize the triggering of theacquisition or radiation after a pre-set lapse of time following themoment when the correspondence is established between the stored andmeasured trigger values.
 7. The drive device according to claim 1,comprising a means for viewing the patients respiratory curve connectedto the control unit and placed so as to be viewable by the operator, andmeans for communicating between the operator and the patient that areable to allow said patient to be informed of the moment when themeasured and stored resting values correspond.
 8. The drive deviceaccording to claim 1, wherein the communication means include a controlbutton to switch on a light on the patient's viewing means.
 9. The drivedevice according to claim 1, wherein the control unit is programmed soas to activate the imaging or radiotherapy unit automatically when thereis a correspondence between the measured and stored trigger values. 10.The drive device according to claim 1, comprising an intermediaryhousing interposed between the control unit and the imaging orradiotherapy unit, and comprising an emergency stop button that can beactivated by an operator.